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 * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.lang.reflect;

import java.lang.annotation.Annotation;
import java.lang.annotation.AnnotationFormatError;
import java.lang.annotation.Repeatable;
import java.util.Arrays;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Objects;
import java.util.function.Function;
import java.util.stream.Collectors;
import sun.reflect.annotation.AnnotationSupport;
import sun.reflect.annotation.AnnotationType;

/**
 * Represents an annotated element of the program currently running in this VM.  This interface
 * allows annotations to be read reflectively.  All annotations returned by methods in this
 * interface are immutable and serializable. The arrays returned by methods of this interface may be
 * modified by callers without affecting the arrays returned to other callers.
 *
 * <p>The {@link #getAnnotationsByType(Class)} and {@link #getDeclaredAnnotationsByType(Class)}
 * methods support multiple annotations of the same type on an element. If the argument to either
 * method is a repeatable annotation type (JLS 9.6), then the method will "look through" a container
 * annotation (JLS 9.7), if present, and return any annotations inside the container. Container
 * annotations may be generated at compile-time to wrap multiple annotations of the argument type.
 *
 * <p>The terms <em>directly present</em>, <em>indirectly present</em>, <em>present</em>, and
 * <em>associated</em> are used throughout this interface to describe precisely which annotations
 * are returned by methods:
 *
 * <ul>
 *
 * <li> An annotation <i>A</i> is <em>directly present</em> on an element <i>E</i> if <i>E</i> has a
 * {@code RuntimeVisibleAnnotations} or {@code RuntimeVisibleParameterAnnotations} or {@code
 * RuntimeVisibleTypeAnnotations} attribute, and the attribute contains <i>A</i>.
 *
 * <li>An annotation <i>A</i> is <em>indirectly present</em> on an element <i>E</i> if <i>E</i> has
 * a {@code RuntimeVisibleAnnotations} or {@code RuntimeVisibleParameterAnnotations} or {@code
 * RuntimeVisibleTypeAnnotations} attribute, and <i>A</i> 's type is repeatable, and the attribute
 * contains exactly one annotation whose value element contains <i>A</i> and whose type is the
 * containing annotation type of <i>A</i> 's type.
 *
 * <li>An annotation <i>A</i> is present on an element <i>E</i> if either:
 *
 * <ul>
 *
 * <li><i>A</i> is directly present on <i>E</i>; or
 *
 * <li>No annotation of <i>A</i> 's type is directly present on <i>E</i>, and <i>E</i> is a class,
 * and <i>A</i> 's type is inheritable, and <i>A</i> is present on the superclass of <i>E</i>.
 *
 * </ul>
 *
 * <li>An annotation <i>A</i> is <em>associated</em> with an element <i>E</i> if either:
 *
 * <ul>
 *
 * <li><i>A</i> is directly or indirectly present on <i>E</i>; or
 *
 * <li>No annotation of <i>A</i> 's type is directly or indirectly present on <i>E</i>, and <i>E</i>
 * is a class, and <i>A</i>'s type is inheritable, and <i>A</i> is associated with the superclass of
 * <i>E</i>.
 *
 * </ul>
 *
 * </ul>
 *
 * <p>The table below summarizes which kind of annotation presence different methods in this
 * interface examine.
 *
 * <table border> <caption>Overview of kind of presence detected by different AnnotatedElement
 * methods</caption> <tr><th colspan=2></th><th colspan=4>Kind of Presence</th> <tr><th
 * colspan=2>Method</th><th>Directly Present</th><th>Indirectly Present</th><th>Present</th><th>Associated</th>
 * <tr><td align=right>{@code T}</td><td>{@link #getAnnotation(Class) getAnnotation(Class&lt;T&gt;)}
 * <td></td><td></td><td>X</td><td></td> </tr> <tr><td align=right>{@code
 * Annotation[]}</td><td>{@link #getAnnotations getAnnotations()} <td></td><td></td><td>X</td><td></td>
 * </tr> <tr><td align=right>{@code T[]}</td><td>{@link #getAnnotationsByType(Class)
 * getAnnotationsByType(Class&lt;T&gt;)} <td></td><td></td><td></td><td>X</td> </tr> <tr><td
 * align=right>{@code T}</td><td>{@link #getDeclaredAnnotation(Class)
 * getDeclaredAnnotation(Class&lt;T&gt;)} <td>X</td><td></td><td></td><td></td> </tr> <tr><td
 * align=right>{@code Annotation[]}</td><td>{@link #getDeclaredAnnotations getDeclaredAnnotations()}
 * <td>X</td><td></td><td></td><td></td> </tr> <tr><td align=right>{@code T[]}</td><td>{@link
 * #getDeclaredAnnotationsByType(Class) getDeclaredAnnotationsByType(Class&lt;T&gt;)}
 * <td>X</td><td>X</td><td></td><td></td> </tr> </table>
 *
 * <p>For an invocation of {@code get[Declared]AnnotationsByType( Class < T >)}, the order of
 * annotations which are directly or indirectly present on an element <i>E</i> is computed as if
 * indirectly present annotations on <i>E</i> are directly present on <i>E</i> in place of their
 * container annotation, in the order in which they appear in the value element of the container
 * annotation.
 *
 * <p>There are several compatibility concerns to keep in mind if an annotation type <i>T</i> is
 * originally <em>not</em> repeatable and later modified to be repeatable.
 *
 * The containing annotation type for <i>T</i> is <i>TC</i>.
 *
 * <ul>
 *
 * <li>Modifying <i>T</i> to be repeatable is source and binary compatible with existing uses of
 * <i>T</i> and with existing uses of <i>TC</i>.
 *
 * That is, for source compatibility, source code with annotations of type <i>T</i> or of type
 * <i>TC</i> will still compile. For binary compatibility, class files with annotations of type
 * <i>T</i> or of type <i>TC</i> (or with other kinds of uses of type <i>T</i> or of type <i>TC</i>)
 * will link against the modified version of <i>T</i> if they linked against the earlier version.
 *
 * (An annotation type <i>TC</i> may informally serve as an acting containing annotation type before
 * <i>T</i> is modified to be formally repeatable. Alternatively, when <i>T</i> is made repeatable,
 * <i>TC</i> can be introduced as a new type.)
 *
 * <li>If an annotation type <i>TC</i> is present on an element, and <i>T</i> is modified to be
 * repeatable with <i>TC</i> as its containing annotation type then:
 *
 * <ul>
 *
 * <li>The change to <i>T</i> is behaviorally compatible with respect to the {@code
 * get[Declared]Annotation(Class<T>)} (called with an argument of <i>T</i> or <i>TC</i>) and {@code
 * get[Declared]Annotations()} methods because the results of the methods will not change due to
 * <i>TC</i> becoming the containing annotation type for <i>T</i>.
 *
 * <li>The change to <i>T</i> changes the results of the {@code get[Declared]AnnotationsByType(Class<T>)}
 * methods called with an argument of <i>T</i>, because those methods will now recognize an
 * annotation of type <i>TC</i> as a container annotation for <i>T</i> and will "look through" it to
 * expose annotations of type <i>T</i>.
 *
 * </ul>
 *
 * <li>If an annotation of type <i>T</i> is present on an element and <i>T</i> is made repeatable
 * and more annotations of type <i>T</i> are added to the element:
 *
 * <ul>
 *
 * <li> The addition of the annotations of type <i>T</i> is both source compatible and binary
 * compatible.
 *
 * <li>The addition of the annotations of type <i>T</i> changes the results of the {@code
 * get[Declared]Annotation(Class<T>)} methods and {@code get[Declared]Annotations()} methods,
 * because those methods will now only see a container annotation on the element and not see an
 * annotation of type <i>T</i>.
 *
 * <li>The addition of the annotations of type <i>T</i> changes the results of the {@code
 * get[Declared]AnnotationsByType(Class<T>)} methods, because their results will expose the
 * additional annotations of type <i>T</i> whereas previously they exposed only a single annotation
 * of type <i>T</i>.
 *
 * </ul>
 *
 * </ul>
 *
 * <p>If an annotation returned by a method in this interface contains (directly or indirectly) a
 * {@link Class}-valued member referring to a class that is not accessible in this VM, attempting to
 * read the class by calling the relevant Class-returning method on the returned annotation will
 * result in a {@link TypeNotPresentException}.
 *
 * <p>Similarly, attempting to read an enum-valued member will result in a {@link
 * EnumConstantNotPresentException} if the enum constant in the annotation is no longer present in
 * the enum type.
 *
 * <p>If an annotation type <i>T</i> is (meta-)annotated with an {@code @Repeatable} annotation
 * whose value element indicates a type <i>TC</i>, but <i>TC</i> does not declare a {@code value()}
 * method with a return type of <i>T</i>{@code []}, then an exception of type {@link
 * java.lang.annotation.AnnotationFormatError} is thrown.
 *
 * <p>Finally, attempting to read a member whose definition has evolved incompatibly will result in
 * a {@link java.lang.annotation.AnnotationTypeMismatchException} or an {@link
 * java.lang.annotation.IncompleteAnnotationException}.
 *
 * @author Josh Bloch
 * @see java.lang.EnumConstantNotPresentException
 * @see java.lang.TypeNotPresentException
 * @see AnnotationFormatError
 * @see java.lang.annotation.AnnotationTypeMismatchException
 * @see java.lang.annotation.IncompleteAnnotationException
 * @since 1.5
 */
public interface AnnotatedElement {

  /**
   * Returns true if an annotation for the specified type
   * is <em>present</em> on this element, else false.  This method
   * is designed primarily for convenient access to marker annotations.
   *
   * <p>The truth value returned by this method is equivalent to:
   * {@code getAnnotation(annotationClass) != null}
   *
   * <p>The body of the default method is specified to be the code
   * above.
   *
   * @param annotationClass the Class object corresponding to the annotation type
   * @return true if an annotation for the specified annotation type is present on this element,
   * else false
   * @throws NullPointerException if the given annotation class is null
   * @since 1.5
   */
  default boolean isAnnotationPresent(Class<? extends Annotation> annotationClass) {
    return getAnnotation(annotationClass) != null;
  }

  /**
   * Returns this element's annotation for the specified type if
   * such an annotation is <em>present</em>, else null.
   *
   * @param <T> the type of the annotation to query for and return if present
   * @param annotationClass the Class object corresponding to the annotation type
   * @return this element's annotation for the specified annotation type if present on this element,
   * else null
   * @throws NullPointerException if the given annotation class is null
   * @since 1.5
   */
  <T extends Annotation> T getAnnotation(Class<T> annotationClass);

  /**
   * Returns annotations that are <em>present</em> on this element.
   *
   * If there are no annotations <em>present</em> on this element, the return
   * value is an array of length 0.
   *
   * The caller of this method is free to modify the returned array; it will
   * have no effect on the arrays returned to other callers.
   *
   * @return annotations present on this element
   * @since 1.5
   */
  Annotation[] getAnnotations();

  /**
   * Returns annotations that are <em>associated</em> with this element.
   *
   * If there are no annotations <em>associated</em> with this element, the return
   * value is an array of length 0.
   *
   * The difference between this method and {@link #getAnnotation(Class)}
   * is that this method detects if its argument is a <em>repeatable
   * annotation type</em> (JLS 9.6), and if so, attempts to find one or
   * more annotations of that type by "looking through" a container
   * annotation.
   *
   * The caller of this method is free to modify the returned array; it will
   * have no effect on the arrays returned to other callers.
   *
   * @param <T> the type of the annotation to query for and return if present
   * @param annotationClass the Class object corresponding to the annotation type
   * @return all this element's annotations for the specified annotation type if associated with
   * this element, else an array of length zero
   * @throws NullPointerException if the given annotation class is null
   * @implSpec The default implementation first calls {@link #getDeclaredAnnotationsByType(Class)}
   * passing {@code annotationClass} as the argument. If the returned array has length greater than
   * zero, the array is returned. If the returned array is zero-length and this {@code
   * AnnotatedElement} is a class and the argument type is an inheritable annotation type, and the
   * superclass of this {@code AnnotatedElement} is non-null, then the returned result is the result
   * of calling {@link #getAnnotationsByType(Class)} on the superclass with {@code annotationClass}
   * as the argument. Otherwise, a zero-length array is returned.
   * @since 1.8
   */
  default <T extends Annotation> T[] getAnnotationsByType(Class<T> annotationClass) {
         /*
          * Definition of associated: directly or indirectly present OR
          * neither directly nor indirectly present AND the element is
          * a Class, the annotation type is inheritable, and the
          * annotation type is associated with the superclass of the
          * element.
          */
    T[] result = getDeclaredAnnotationsByType(annotationClass);

    if (result.length == 0 && // Neither directly nor indirectly present
        this instanceof Class && // the element is a class
        AnnotationType.getInstance(annotationClass).isInherited()) { // Inheritable
      Class<?> superClass = ((Class<?>) this).getSuperclass();
      if (superClass != null) {
        // Determine if the annotation is associated with the
        // superclass
        result = superClass.getAnnotationsByType(annotationClass);
      }
    }

    return result;
  }

  /**
   * Returns this element's annotation for the specified type if
   * such an annotation is <em>directly present</em>, else null.
   *
   * This method ignores inherited annotations. (Returns null if no
   * annotations are directly present on this element.)
   *
   * @param <T> the type of the annotation to query for and return if directly present
   * @param annotationClass the Class object corresponding to the annotation type
   * @return this element's annotation for the specified annotation type if directly present on this
   * element, else null
   * @throws NullPointerException if the given annotation class is null
   * @implSpec The default implementation first performs a null check and then loops over the
   * results of {@link #getDeclaredAnnotations} returning the first annotation whose annotation type
   * matches the argument type.
   * @since 1.8
   */
  default <T extends Annotation> T getDeclaredAnnotation(Class<T> annotationClass) {
    Objects.requireNonNull(annotationClass);
    // Loop over all directly-present annotations looking for a matching one
    for (Annotation annotation : getDeclaredAnnotations()) {
      if (annotationClass.equals(annotation.annotationType())) {
        // More robust to do a dynamic cast at runtime instead
        // of compile-time only.
        return annotationClass.cast(annotation);
      }
    }
    return null;
  }

  /**
   * Returns this element's annotation(s) for the specified type if
   * such annotations are either <em>directly present</em> or
   * <em>indirectly present</em>. This method ignores inherited
   * annotations.
   *
   * If there are no specified annotations directly or indirectly
   * present on this element, the return value is an array of length
   * 0.
   *
   * The difference between this method and {@link
   * #getDeclaredAnnotation(Class)} is that this method detects if its
   * argument is a <em>repeatable annotation type</em> (JLS 9.6), and if so,
   * attempts to find one or more annotations of that type by "looking
   * through" a container annotation if one is present.
   *
   * The caller of this method is free to modify the returned array; it will
   * have no effect on the arrays returned to other callers.
   *
   * @param <T> the type of the annotation to query for and return if directly or indirectly
   * present
   * @param annotationClass the Class object corresponding to the annotation type
   * @return all this element's annotations for the specified annotation type if directly or
   * indirectly present on this element, else an array of length zero
   * @throws NullPointerException if the given annotation class is null
   * @implSpec The default implementation may call {@link #getDeclaredAnnotation(Class)} one or more
   * times to find a directly present annotation and, if the annotation type is repeatable, to find
   * a container annotation. If annotations of the annotation type {@code annotationClass} are found
   * to be both directly and indirectly present, then {@link #getDeclaredAnnotations()} will get
   * called to determine the order of the elements in the returned array.
   *
   * <p>Alternatively, the default implementation may call {@link #getDeclaredAnnotations()} a
   * single time and the returned array examined for both directly and indirectly present
   * annotations. The results of calling {@link #getDeclaredAnnotations()} are assumed to be
   * consistent with the results of calling {@link #getDeclaredAnnotation(Class)}.
   * @since 1.8
   */
  default <T extends Annotation> T[] getDeclaredAnnotationsByType(Class<T> annotationClass) {
    Objects.requireNonNull(annotationClass);
    return AnnotationSupport.
        getDirectlyAndIndirectlyPresent(Arrays.stream(getDeclaredAnnotations()).
                collect(Collectors.toMap(Annotation::annotationType,
                    Function.identity(),
                    ((first, second) -> first),
                    LinkedHashMap::new)),
            annotationClass);
  }

  /**
   * Returns annotations that are <em>directly present</em> on this element.
   * This method ignores inherited annotations.
   *
   * If there are no annotations <em>directly present</em> on this element,
   * the return value is an array of length 0.
   *
   * The caller of this method is free to modify the returned array; it will
   * have no effect on the arrays returned to other callers.
   *
   * @return annotations directly present on this element
   * @since 1.5
   */
  Annotation[] getDeclaredAnnotations();
}
